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89 F150 Oil Pressure Question

So I’ve done a bunch of looking around for what, I hope, to be a good answer to this and basically what I’ve heard is that “If you have it, it’s good… if you don’t, it’s bad.” - Super helpful that.

My 89 F150, upon first start is showing about 40-50 psi on the after market gauge that was installed in the truck. After the truck get’s up to running temp, it drops waaaay down to 10 or less.

What would be considered optimal oil pressure and what’s the best way to go about getting the vehicle up to that? I know that’s a tricky question… I’ve been trying to find some better information for a while and it’s been kinda hit and miss. I believe there may be a leak in there somewhere, I do get some drips from time to time… not always… but it’s not a huge leak so I’m not assuming there’s a big hole in anything. Plus I don’t seem to have to replace oil at any regular interval.

My commute has gone from about 2 minutes to 20 minutes recently and I’d kinda like to make sure I’m not putting any extra strain on this near 30 year old engine. I’m going to be getting something else as my commuter vehicle in a few months but it’s still not a bad truck and if I can keep it around I will.

Anyway… that’s enough out of me. Thoughts? And thanks in advance.

I would begin by having the oil pressure measured with a mechanical gauge by a mechanic to determine if it is the guage or a problem in the engine. It is possible that it might be the sending unit for the gauge which may be cause of your oil leak. If the pressure falls off when measured with the mechanical gauge, then it could be main bearings, camshaft bearings or the oil pump.

The oil pressure spec for your engine is 50 PSI @ 2,000 RPM’s.


External oil leaks, like drips onto the ground, have nothing to do with the oil pressure in the engine, as long as the level is in the safe zone.

The pressure should be tested with a mechanical gauge.

It’s normal for engine oil pressure to be high when you first start a cold engine, and then to drop as the engine warms up. An old rule of thumb for a fully warmed up engine is 10 psi of oil pressure for every 1,000 rpm. So you’d want about 10 psi at idle and 30 psi at 3000 rpm.

If the oil pressure is low there’s nothing you can do to fix it that doesn’t require engine work. There’s nothing external you can do.

I suspect the crankshaft and possibly the camshaft bearings are worn and leading to abnormally low oil pressure when the oil is up to operating temps.
Ten PSI is too low on what I assume is a 5.0 engine.

Odds are if you drop the oil pan and remove a few bearings caps on the end fartherest away from the oil pump you will probably find the bearing shells are down into the copper.

Don’t interpret Tester’s post as meaning the oil pressure should also be 50PSI at idle. He’s giving you the correct spec to test if it’s building to the proper spec at the proper RPM, which evaluates the condition of the lubrication system overall. 10PSI at idle on a warm engine when the oil is at its thinnest would not be unusually low. You need to check it at the RPM that tester specified.

I support ase’s post. The pump pushes the oil through channels inside the engine’s parts and develops pressure by forcing the oil through the small spaces between the bearings and their corresponding surfaces. If the wear gets to the point that these spaces are too big, the oil flows through too easily and the pump can not longer maintain pressure. The symptoms usually show up initially when the oil is at its thinnest, when it’s at operating temp. The pump’s challenge at that point is sort of like trying to maintain pressure in a tire with a screw hole… after the screw’s pulled out.

The only solution is to reface (or replace) the wear surfaces that have worn, using parts with specifications altered to accommodate the newly-sized parts.

It should also be noted that the oil pump is a simple system of interlocked impellars that spend their entire lives bathed in fresh, constantly-flowing oil. They don’t generally wear out, and an oil pump replacement is not the answer to low pressure. If this is suggested by anyone, I recommend you go elsewhere.

There was a local mechanic here who is now deceased and he was mostly a lifelong Ford man.

I’m not privy to how many low oil pressure Fords he messed around with but I know that it was many. The complaint would be oil light on or low oil pressure on the gauge.
He would always throw parts at it in this order.

  1. Oil pressure sending unit.
  2. Oil pump.
  3. Crank bearings.

That begs the question of why in the hxxx if you’re dropping the pan to replace an oil pump then why not drop some bearing caps and check the bearings instead of replacing the pump, reassembling it, and then tearing it back down again to replace bearings.

Job security I guess… :wink:

Interesting question. Excellent suspicion. :lol:

I always wondered why so many people blame the oil pump when the pressure is low. I always attributed it to a lack of knowledge. This guy sounds like he should have had the knowledge.

Check your owner’s manual and see if you can bump up the weight of your engine oil. You will be surprised at the difference it makes in your oil pressure readings.

I can’t speak to the specifics of your truck, but my early 70’s Ford truck (302 v8) with a dash oil pressure gauge shows an oil pressure of around 40 when first started, and tends to rise to around 50-60 when driving at speed. It never shows anything as low as 10 while the engine is running, except possibly when first started in very cold weather.

My commute has gone from about 2 minutes to 20 minutes recently and I'd kinda like to make sure I'm not putting any extra strain on this near 30 year old engine.

A 2-minute commute is much harder on an engine than a 20-minute one. The engine never comes up to full operating temperature long enough to boil off any condensation, if at all.